Re-directing Help>Manual Menu to Local Drive
Two ways I can see to achieve this.

1 Manually edit the UI script

Either manually edit the space_topbar.py topbar UI file traditionally found at Blender_2.82\2.82\scripts\startup\bl_ui\space_topbar.py and type in an entry there to link to your local file.

You can optionally remove the online manual entry from there and replace it with an instance of wm.url_open operator pointing to your local file. Just copy one of the existing templates and modify it to your own use.

This is a quick and dirty solution, allows removing the existing entry, but is less maintainable, since it will likely not survive a software update nor is it easy to port to other installations.

2 Create a script or addon

Create a script that registers a new menu entry with a link to your own file. Easiest is probably to use wm.url_open operator pointing to your local file.



import bpy

def menu_func(self, context):
    self.layout.operator(
            "wm.url_open", text="Local Maual", icon='HELP',
        ).url = "Z:/Applications/Blender/Documentation/Blender_Manual.pdf"


def register():
    bpy.types.TOPBAR_MT_help.append(menu_func)


def unregister():
    bpy.types.TOPBAR_MT_help.remove(menu_func)


if __name__ == "__main__":
    register()


As far as I know this won't allow removing the existing entry, but you can have the addon under, several instances, and can easily be reinstalled after software updates.